1. Technical Field
The invention relates to a circuit configuration for a digital-to-analog converter and an analog-to-digital converter with an R2R resistive network and voltage comparators, preferably for inkjet printers.
2. Background Art
In modern inkjet printers employing the bubble-jet principle, the ink droplets are generated by heating resistors incorporated into the inkjet print head, see for example, German Patent Publication DE-OS 3 012 698. It is important that the heating pulses lie within given limits in order both to achieve the desired function (i.e., to properly generate ink droplets) and to protect the inkjet print head from damage. Inkjet print heads must not be allowed to get too hot, see, e.g., PCT Patent Publication WO 90/06852. The print head temperature, therefore, has to be monitored. The monitoring is performed using sensors which supply analog voltages corresponding to the temperatures of the print heads. Analog-to-digital (A/D) converters with reference voltage sources and comparators are required to digitally evaluate these voltages, see, e.g., the machine description "High Print 6200" print head control, page 4--4, FIG. 4-2, Siemens AG 1990.
On the other hand, in modern inkjet printers, it is common to use a DC motor controlled by a motor driver circuit for the carriage drive. This motor driver circuit, in turn, receives its control voltage via a digital-to-analog (D/A) converter with an R2R network as well as a reference voltage source and a comparator, see, e.g., the machine description "High Print 6200", print head carriage drive, page 4; see also, the machine description "High Print 6200", print head control, page 4-1, FIG. 4-1, Siemens AG 1990. The precision of the digital-to-analog voltage conversion depends significantly on the precision of the reference voltage. Precision voltage sources, however, are expensive.
Although a common digital logic (e.g., microcontroller, ASIC, discrete logic IC's, etc.) is used for the head control and carriage drive control, the amount of electronics used is still considerable. For cost reasons, a precise reference voltage is therefore dispensed with for the carriage drive control. Instead, the carriage drive control is fed directly with the output voltage from the digital logic--corresponding to TTL or CMOS level. Using this output voltage directly results in inaccuracies of up to 100% which can be compensated with an appropriate degree of control engineering.